In internal combustion engines, it is known that during operation a certain residual gas mass remains in the cylinder, i.e., even after combustion and during opening of an exhaust valve of the cylinder. The residual gas, or also the cylinder residual gas, is formed by exhaust gas.
It is known that the cylinder residual gas mass may be composed of various portions. On the one hand, a cylinder typically has a cylinder clearance volume that is always filled with cylinder residual gas and is not emptied. On the other hand, so-called internal exhaust gas recirculation is known in which, as the result of a (desired) valve overlap, i.e., an intake and exhaust valve (or valves) that are open at the same time, exhaust gas passes from an exhaust tract (exhaust manifold, for example) via the combustion chamber of the cylinder and into an intake tract (intake manifold, for example). The residual gas mass in the cylinder may be further increased in this way.
The cylinder residual gas mass calculated in an engine control unit is typically crucial for precisely determining the cylinder air mass, whose detection as accurately as possible is the prerequisite for stoichiometric fuel injection. A stoichiometric air-fuel ratio may be used to reduce the exhaust emissions after appropriate exhaust gas aftertreatment.
For physical models as well as parameterized models, measured parameters and model parameters, such as the speed of the internal combustion engine, the phase position of a camshaft, a valve position, and the like, are typically included in the calculation of the cylinder residual gas mass. In addition, the exhaust gas temperature is also typically included as a parameter in such models.
It is known that data for the parameters may be input on an engine-specific basis by the use of stationary engine test stand measurements under standard conditions. However, during dynamic operation of an internal combustion engine, insufficient thermal relaxation times in the exhaust gas temperatures or the like, due to ignition angle interventions, may result in deviations from the measured stationary operation, so that the calculated cylinder residual gas mass may become inaccurate.
For physical models as well as parameterized models, it is known to take into account deviating exhaust gas temperatures by the engine-specific input of data parameters in the overall model for calculating the cylinder residual [gas] mass, which, however, is typically complicated and may require high computing power and a large memory.
It is also known from German unexamined patent application DE 10 2005 055 952 A1 that the relationship between air charging in a combustion chamber of a cylinder and a measured intake manifold pressure is not linear. To obtain a simple, accurate determination of the air mass present in the combustion chamber, the unexamined patent application proposes to determine a residual gas partial pressure of the residual gas present in the combustion chamber. In addition, the air partial pressure of the air present in the combustion chamber is determined as a function of the residual gas partial pressure. The air mass in the combustion chamber is then determined as a function of the residual gas partial pressure.
The methods known in the prior art for determining the residual gas mass, which are based on parameterized models, for example, have the disadvantage that the number of model input parameters generally exponentially increases the memory and computing requirements for the engine control unit. When exhaust gas temperatures that deviate from those in stationary operation are taken into account, the level of measurement and application effort increases.